Microphone system



bec. 1s, 192s. 1,695,875' J. E. AIKEN uIcRoPHoNE ssmu Filed mi2, 1925 wlmasslas;l INVENTQR Jose/oh E. A/en.

'Y l BY ATTORNEY for.

Patented Dec. 18, 1928.

UNITED STATES PATENT" OFFICE.

` JOSEPH E. AIKEN, 0F WLKINSBUBG, PENNSYLVANIA, ASSIGNOB T0 WIES'IIIINGHOUSIE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION 0F PENNSYLVANIA.

MICROPHONE SYSTEM.

Application tiled July 2, 1925. Serial- No. 41,179. y

My invention relates to microphone systems and particularly to regulating means there- An object of my invention is to provide a balancing means for regulating the output of a tduplex or double button microphone.

fAnother object of my -invention is to provide aconvenient means for controllingthe current value through the opposite resistors in a duplex microphone.

Another object of my invention is to provide a regulating means having resistor elements which are alternatively effective under the control of contact armswhich are simultaneously movable. Y

In the operation of duplex microphones, it has been found that frequently there is a difference in the quiet resistance of the granules in the respective granule cups on opposite sides of the diaphragm. This difference in resistance appears to be due to minor differences in the quantity of granules in the cups and to minor differences in the tightness of packing.- It results in differences in the currentvalue in the opposite respective granule resistors and thus results in differences in the variable-current component produced.

It is well known that the single resistors of a'microphone do not give strict proportionality of translation of sound vibrations into electrical vibrations, but it has been found possible, by the use of two microphone resistors operated by a single diaphragm, as in the duplex type, to cause the deviation of the change in resistance from strict proportionality to occur 1n opposite dlrections and therev by to neutralize each other. This occurs only when the'current through the two resistors is the same.

. and.' apparatus of the system of my. invention.

I provide, as apart' of my invention, a rheostat, shown in Fig. 1 and having a base portion 1, a contact arm 2 attached to ashaft 3, and moving'over a resistance winding 4 and a non-resistive contact bar 5 connected thereto. i y

In acomplete rheostat, two of the members shown in' Fig. 1 are mounted face-.to-face, as shown in Fig. 2. The base member 1 of each rheostat is attached to a metal frame 6 which frames are connected by insulating members 7 and screws 8. The base member 1 of the outer rheostat is clamped against its frame 6 by screws 9 which may pass through a supporting plate 10. An insulating coupling 11 is provided between the shafts 3 of the-respective rheostats and serves to cause vthe contact arms 2 to move simultaneously under the control of a knob 12. The positionof the contact arms is indicated by a pointer 14.

The duplex rheostat device of Fig. 2' is shown diagrammatically at 15 in Fig. 3, with suitable circuit connections thereto. i

Referring to Fig. 3, a double-button microphone has a frame 16, a diaphragm 17 and tions are made from the respective contact arms 2 to a switching device 24.

The device24 may be aptly described as a quadruple-pole, 'double-throw switch, comprising switch blades 40, 41, 42 and 43 and associated active contact elements 44, 45, 46, 47 48 and 49. .A conductor 51 connects the inner contact arm 2 tothe blade 40, and to the contact element 47 and a Conductor 52 connects the outer contact arm 2 to the contact elements'44 and 48. In'one position of the device 24, acircuit may be traced fromY the resistor 22 through the diaphragm 1 7, resistor 18, outer rheostat element 5, the inner contact arm 2, conductor 51, contact 47, switeh blade 42, ammeter 31, arm 43, upper primary winding of the transformer 27, battery 23 and back to the resistorv 22. Another circuit may be traced from the resistor 22,y throughv the diaphragm 17, resistor 19, inner rheostat element y5, outer contact vious on inspection of the drawing.

Attention is called to the fact, however, that, by a simple movement of the switching device, the ammeter may be included in circuit with either of the microphone resistors, thus permitting an observation to be made of the current flowing therethrough.

'Ihe rheostat 15 is so assembled that the midposition of the contacts 2 provides a point at which no resistance is included in either of the circuits to the resistors 18 and 19. By means of this construction, a slight movement of the knob in either direction will selectively insert resistance gradually into one only of the resistor circuits and in accordance with the direction of movement.

In the operation of my device, the rheostat 22 may be so adjusted, with the ammeter 31 in one ol' the resistor circuits, that the reading of the ammeter 31 is about one hall' of the desired total current through the microphone. rIhe rheostat 15 may then be adjusted to the one or the other side of its midposition until, upon changing the ammeter 31 from one circuit to the other, it shows that equal currents are flowing through the resistors 18 and 19.

By mea-ns of my invention, I am enabled to provide a duplex microphone system containing a special rheostat, by means of which it is possible to adjust the variable-component output of the microphone members in such way as to obtain precise neutralization of the irregularities produced by the device, and I have further provided indicating means whereby this condition of equality may be demonstrated.

lVhile I have shown but a single embodiment ot' my invention in the accmnpanying description, it is capable et various modifications therefrom, and it is desired, therefore, that only such limitations shall bev imposed thereon as are required by the prior art or indicated in the appended claims.

I claim as my invention:

1. Regulating means for a differential microphone having an input terminal and output terminals comprising a rheostat connected to the input terminal, a duplex rheostat having two sections respectively connected to the output terminals of the microphone and being alternatively insertable in circuit therewith, and common control means for said rheostat.

2. Regulating means for a differential microphone having an input terminal and output terminals comprising a rheostat connected to the input terminal, a duplex rheostat having two sections respectively connected to the output terminals of the microphone and being alternatively insertable in circuit therewith, a single control device for said duplex rheostat, and means for selectively connecting an indicating device to said output terminals.-

3. A microphone system comprising a microphone having two variable-resistance element-s, a transformer having two primary coils oppositely effective and connected, re-

spectively, to said microphone resistors, and

a duplex rheostat connected therebetween having sections that are respectively connected to said microphone resistors, simultaneously operable, and alternately effective.

A4. A microphone system comprising a inicrophone having a single diaphragm and two vibration-responsive resistors respectively on opposite sides thereof, and means respectively connected in circuit'with said resistors to be simultaneously operable and alternately effective to control said resistors.

5. In combination, a differential -microphone, means for simultaneously inserting a resistor in circuit with one of the elements thereof and removing a resistor from a circuit connected to another of the elements, means for supplying talking'current, means for indicating the amount of current flowing in each portion of the microphone, and means for switching the current-indicating means from one to another of the microphone eircuits, whereby the current flowing through the microphone in its quiet state may be cqualized.

In testimony whereof', I have hereunto suhscribed my name this 24th day of June, 19254 JOSEPH E. AIKEN. 

